1. Field of the Invention
The present invention relates to a data communication apparatus, and more particularly to a data communication apparatus having an error correction communication mode.
2. Related Background Art
A facsimile device having an error correction communication mode (ECM communication of the CCITT Recommendation) has been known. In the prior art facsimile communication, a minimum transmission time is set and updated in accordance with the performance of a receiver (such as the decoding performance and printing speed). However, in the ECM communication, communication is made not line by line but block by block and the receiver uses two planes of buffer memory (a maximum frame size is 256 bytes: 256 bytes.times.256 frames.times.2 planes=128K bytes), so that the image is received by one plane while the data correctly received by that buffer plane or the data correctly received previously by the other buffer plane is printed out. In the ECM communication, when a receiving station wants to delay transmission from a transmitting station because of a long time required for the printing, the receiving station sends out to the transmitting station a signal (RNR signal) to delay the transmission of the next block.
However, the CCITT T30 Recommendation defines T5=60.+-.5 seconds. Thus, in an apparatus which takes a long time for decoding or printing, there may be a case when the printing is not completed in the T5 time and the data cannot be correctly received.
A facsimile device having an error retransmission mode is disclosed in U.S. Pat. No. 4,829,524 (issued on May 9, 1989), U.S. Pat. No. 4,885,755 (issued on Dec. 5, 1989), U.S. Pat. No. 4,897,831 (issued on Jan. 30, 1990), U.S. Pat. No. 5,031,179 (issued on Jul. 9, 1991), U.S. Pat. No. 5,075,783 (issued on Dec. 24, 1991), U.S. application Ser. No. 670,934 (filed on Mar. 18, 1991) and U.S. application Ser. No. 371,847 (filed on Jun. 27, 1989).
However, there has been no proposal for the solution of the above problems.